Immunogenic and Antigenic Structure of Porphyromonas gingivalis fimbriae The fimbriate of Porphyromonas gingivalis(Pg) are important virulence factors that mediate adherence to host surfaces. The linear immunogenic and antigenic structure of Pg fimbriae was investigated with synthetic peptides as well as recombinant full length and truncated fimbrillin proteins corresponding to the amino acid sequence predicted form the cloned fimbrillin gene for Pg 381 (Dickinson et al., J. Bact. 170: 1658, 1988). A series of peptides corresponding to the sequential amino acid residues of Pg fimbrillin were synthesized using a solid phase peptide synthesis procedure, coupled to thyroglobulin, and used to immunize Wistar rats. The resulting polyclonal antibodies were utilized to test the antigenicity of the 43 kDa fimbrillin protein of Pg 381 by ELISA and Western blot analysis. All the peptides elicited specific antibodies against corresponding peptides, but differed substantially in their ability to elicit antisera that cross- reacted with either native or denatured fimbriae. Recombinant full and truncated lengths of the fimbrillin have been produced in an E.coli expression system. Rat antiserum made to native fimbria was used inn qualitative and quantitative assay systems to test the cross-reactivity of anti-fimbria sera with the isolated recombinant fimbrillin products. In addition, C-terminal antipeptide sera was used to investigate the cross-reactivity of these polyclonal antibodies with fimbria isolated from various strains of Pg by Western Blot analysis. Key words: Antigaenic determinant, immunodominant epitope, Porphyromonas gingivalis, fimbria, synthetic peptide.